Various existing radar apparatuses have been created. Each radar apparatus is provided at the front, or the like, of an automobile, transmits a transmission wave to a predetermined detecting area including the front area of the automobile, and then receives a wave reflected from a target inside the detecting area, thus detecting the target. Then, in an automotive field, an FMCW radar apparatus is used as the above radar apparatus.
The FMCW radar apparatus generates an IF beat signal by multiplying a transmission signal based on a transmission wave by a reception signal that includes a reflected wave and then detects a target through a complex frequency spectrum of the IF beat signal. At this time, the FMCW radar apparatus applies a known direction of arrival estimation algorithm, such as a beamformer method, to the acquired complex frequency spectrum to thereby estimate the azimuth of the target detected.
However, when the desired target has a relative velocity with respect to a host vehicle (host apparatus), the estimated azimuth includes an error due to the relative velocity. As a solution for this problem, a radar apparatus described in Patent Document 1 separately calculates a relative velocity and then corrects the estimated azimuth on the basis of the calculated relative velocity.
[Patent Document 1] Japanese Patent No. 3575694
However, with the method described in Patent Document 1, when a highly accurate azimuth is intended to be detected, the relative velocity also needs to be accurately detected.
Here, for example, when the frequency of the transmission wave is 76.5 GHz, the time interval at which a plurality of receiving antennas are switched is 1 ms, and the relative velocity of the desired target is 1 km/h, a variation in distance from the target to the receiving antenna between the adjacent receiving antennas due to the relative velocity is about 0.14λ where the wavelength of transmission and reception waves is λ. Here, when the interval between the receiving antennas is 0.9λ, an azimuth error caused by the relative velocity is about 9°.
Thus, even when the relative velocity is just 1 km/h, the phase difference of about 9° occurs. Therefore, to calculate a highly accurate azimuth, a relative velocity further more precise than 1 km/h needs to be calculated. Hence, it is considerably difficult to calculate a highly accurate azimuth with a method of correcting the azimuth using a relative velocity as described in Patent Document 1.